Lithographic apparatus and device manufacturing method

ABSTRACT

In an immersion lithography apparatus in which immersion liquid is supplied to a localized space, the space is substantially polygonal in plan substantially parallel to the substrate. In an embodiment, two corners of the space have a radius of curvature no greater than the width of a transition zone between the space configured to contain liquid and a surrounding configured not to contain liquid.

RELATED APPLICATION

This is a continuation application of co-pending U.S. patent applicationSer. No. 10/986,185, filed Nov. 12, 2004, the entire contents of theforegoing application is hereby incorporated by reference.

FIELD

The present invention relates to a lithographic apparatus and a methodfor manufacturing a device.

BACKGROUND

A lithographic apparatus is a machine that applies a desired patternonto a substrate, usually onto a target portion of the substrate. Alithographic apparatus can be used, for example, in the manufacture ofintegrated circuits (ICs). In that instance, a patterning device, whichis alternatively referred to as a mask or a reticle, may be used togenerate a circuit pattern to be formed on an individual layer of theIC. This pattern can be transferred onto a target portion (e.g.comprising part of, one, or several dies) on a substrate (e.g. a siliconwafer). Transfer of the pattern is typically via imaging onto a layer ofradiation-sensitive material (resist) provided on the substrate. Ingeneral, a single substrate will contain a network of adjacent targetportions that are successively patterned. Known lithographic apparatusinclude so-called steppers, in which each target portion is irradiatedby exposing an entire pattern onto the target portion at one time, andso-called scanners, in which each target portion is irradiated byscanning the pattern through a radiation beam in a given direction (the“scanning”-direction) while synchronously scanning the substrateparallel or anti-parallel to this direction. It is also possible totransfer the pattern from the patterning device to the substrate byimprinting the pattern onto the substrate.

It has been proposed to immerse the substrate in the lithographicprojection apparatus in a liquid having a relatively high refractiveindex, e.g. water, so as to fill a space between the final element ofthe projection system and the substrate. The point of this is to enableimaging of smaller features since the exposure radiation will have ashorter wavelength in the liquid. (The effect of the liquid may also beregarded as increasing the effective NA of the system and alsoincreasing the depth of focus.) Other immersion liquids have beenproposed, including water with solid particles (e.g. quartz) suspendedtherein.

However, submersing the substrate or substrate and substrate table in abath of liquid (see, for example, U.S. Pat. No. 4,509,852, herebyincorporated in its entirety by reference) means that there is a largebody of liquid that must be accelerated during a scanning exposure. Thisrequires additional or more powerful motors and turbulence in the liquidmay lead to undesirable and unpredictable effects.

One of the solutions proposed is for a liquid supply system to provideliquid on only a localized area of the substrate and in between thefinal element of the projection system and the substrate (the substrategenerally has a larger surface area than the final element of theprojection system). One way which has been proposed to arrange for thisis disclosed in PCT patent application WO 99/49504, hereby incorporatedin its entirety by reference. As illustrated in FIGS. 2 and 3, liquid issupplied by at least one inlet IN onto the substrate, preferably alongthe direction of movement of the substrate relative to the finalelement, and is removed by at least one outlet OUT after having passedunder the projection system. That is, as the substrate is scannedbeneath the element in a −X direction, liquid is supplied at the +X sideof the element and taken up at the −X side. FIG. 2 shows the arrangementschematically in which liquid is supplied via inlet IN and is taken upon the other side of the element by outlet OUT which is connected to alow pressure source. In the illustration of FIG. 2 the liquid issupplied along the direction of movement of the substrate relative tothe final element, though this does not need to be the case. Variousorientations and numbers of in- and out-lets positioned around the finalelement are possible, one example is illustrated in FIG. 3 in which foursets of an inlet with an outlet on either side are provided in a regularpattern around the final element.

In an immersion lithographic apparatus in which the immersion liquid islocalized under the projection system, one or more drying stains may beleft on the substrate after the liquid supply system has passed. Suchdrying stains may cause defects in the printed devices and cause otherproblems for several reasons. The drying stains may affect developmentof the exposed resist. Drying stains may prevent proper exposure of theunderlying resist (drying stains caused during exposure of one targetportion or during acceleration and/or deceleration may overlay anadjacent target portion which is exposed later). Particles from dryingstains may chemically contaminate the substrate. Particles from dryingstains may contaminate other parts of the apparatus.

SUMMARY

Accordingly, it would be advantageous, for example, to provide animmersion lithography apparatus in which the occurrence of one or moredrying stains on the substrate is reduced or avoided.

According to an aspect of the invention, there is provided alithographic projection apparatus arranged to project a pattern from apatterning device onto a substrate through a liquid, the apparatuscomprising a liquid confinement structure configured to confine theliquid to a space adjacent the substrate, wherein the space is smallerin plan than the substrate and is substantially polygonal in plansubstantially parallel to the substrate.

-   -   According to an aspect of the invention, there is provided a        lithographic projection apparatus, comprising:

an illuminator configured to condition a radiation beam;

a support constructed to hold a patterning device, the patterning deviceconfigured to impart the radiation beam with a pattern in itscross-section to form a patterned radiation beam;

a substrate table constructed to hold a substrate;

a projection system configured to project the patterned radiation beamonto a target portion of the substrate;

a liquid supply system configured to at least partly fill a spacebetween the projection system and the substrate with a liquid, theliquid supply system comprising a liquid confinement structureconfigured to at least partly confine the liquid within the space, aninner periphery of the liquid confinement structure adjacent the liquidsubstantially forming a polygon.

According to an aspect of the invention, there is provided a devicemanufacturing method, comprising:

supplying liquid to a space adjacent a substrate, the space beingsmaller in plan than the substrate and being substantially polygonal inplan substantially parallel to the substrate; and

projecting a patterned beam of radiation through the liquid onto thesubstrate.

According to an aspect of the invention, there is provided a devicemanufacturing method, comprising:

at least partly confining a liquid to a space between a projectionsystem of a lithographic apparatus and a substrate using a liquidconfinement structure, an inner periphery of the liquid confinementstructure adjacent the liquid substantially forming a polygon; and

projecting a patterned beam of radiation through the liquid onto thesubstrate.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts, and inwhich:

FIG. 1 depicts a lithographic apparatus according to an embodiment ofthe invention;

FIGS. 2 and 3 depict a liquid supply system for use in a lithographicprojection apparatus;

FIG. 4 depicts another liquid supply system for use in a lithographicprojection apparatus;

FIG. 5 depicts a further liquid supply system for use in a lithographicprojection apparatus;

FIG. 6 depicts in plan the liquid supply system of FIG. 5;

FIG. 7 depicts in plan the liquid supply system of an embodiment of theinvention;

FIG. 8 depicts a transition zone between “wet” and “dry” spaces; and

FIG. 9 depicts alternative shapes of the liquid-filled space.

DETAILED DESCRIPTION

FIG. 1 schematically depicts a lithographic apparatus according to anembodiment of the invention. The apparatus comprises:

-   -   an illumination system (illuminator) IL configured to condition        a radiation beam PB (e.g. UV radiation or DUV radiation).    -   a support structure (e.g. a mask table) MT constructed to hold a        patterning device (e.g. a mask) MA and connected to a first        positioner PM configured to accurately position the patterning        device in accordance with certain parameters;    -   a substrate table (e.g. a wafer table) WT constructed to hold a        substrate (e.g. a resist-coated wafer) W and connected to a        second positioner PW configured to accurately position the        substrate in accordance with certain parameters; and    -   a projection system (e.g. a refractive projection lens system)        PL configured to project a pattern imparted to the radiation        beam PB by patterning device MA onto a target portion C (e.g.        comprising one or more dies) of the substrate W.

The illumination system may include various types of optical components,such as refractive, reflective, magnetic, electromagnetic, electrostaticor other types of optical components, or any combination thereof, fordirecting, shaping, or controlling radiation.

The support structure holds the patterning device in a manner thatdepends on the orientation of the patterning device, the design of thelithographic apparatus, and other conditions, such as for examplewhether or not the patterning device is held in a vacuum environment.The support structure can use mechanical, vacuum, electrostatic or otherclamping techniques to hold the patterning device. The support structuremay be a frame or a table, for example, which may be fixed or movable asrequired. The support structure may ensure that the patterning device isat a desired position, for example with respect to the projectionsystem. Any use of the terms “reticle” or “mask” herein may beconsidered synonymous with the more general term “patterning device.”

The term “patterning device” used herein should be broadly interpretedas referring to any device that can be used to impart a radiation beamwith a pattern in its cross-section such as to create a pattern in atarget portion of the substrate. It should be noted that the patternimparted to the radiation beam may not exactly correspond to the desiredpattern in the target portion of the substrate, for example if thepattern includes phase-shifting features or so called assist features.Generally, the pattern imparted to the radiation beam will correspond toa particular functional layer in a device being created in the targetportion, such as an integrated circuit.

The patterning device may be transmissive or reflective. Examples ofpatterning devices include masks, programmable mirror arrays, andprogrammable LCD panels. Masks are well known in lithography, andinclude mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. An exampleof a programmable mirror array employs a matrix arrangement of smallmirrors, each of which can be individually tilted so as to reflect anincoming radiation beam in different directions. The tilted mirrorsimpart a pattern in a radiation beam which is reflected by the mirrormatrix.

The term “projection system” used herein should be broadly interpretedas encompassing any type of projection system, including refractive,reflective, catadioptric, magnetic, electromagnetic and electrostaticoptical systems, or any combination thereof, as appropriate for theexposure radiation being used, or for other factors such as the use ofan immersion liquid or the use of a vacuum. Any use of the term“projection lens” herein may be considered as synonymous with the moregeneral term “projection system”.

As here depicted, the apparatus is of a transmissive type (e.g.employing a transmissive mask). Alternatively, the apparatus may be of areflective type (e.g. employing a programmable mirror array of a type asreferred to above, or employing a reflective mask).

The lithographic apparatus may be of a type having two (dual stage) ormore substrate tables (and/or two or more mask tables). In such“multiple stage” machines the additional tables may be used in parallel,or preparatory steps may be carried out on one or more tables while oneor more other tables are being used for exposure.

Referring to FIG. 1, the illuminator IL receives a radiation beam from aradiation source SO. The source and the lithographic apparatus may beseparate entities, for example when the source is an excimer laser. Insuch cases, the source is not considered to form part of thelithographic apparatus and the radiation beam is passed from the sourceSO to the illuminator IL with the aid of a beam delivery system BDcomprising, for example, suitable directing mirrors and/or a beamexpander. In other cases the source may be an integral part of thelithographic apparatus, for example when the source is a mercury lamp.The source SO and the illuminator IL, together with the beam deliverysystem BD if required, may be referred to as a radiation system.

The illuminator IL may comprise an adjuster AD for adjusting the angularintensity distribution of the radiation beam. Generally, at least theouter and/or inner radial extent (commonly referred to as σ-outer andσ-inner, respectively) of the intensity distribution in a pupil plane ofthe illuminator can be adjusted. In addition, the illuminator IL maycomprise various other components, such as an integrator IN and acondenser CO. The illuminator may be used to condition the radiationbeam, to have a desired uniformity and intensity distribution in itscross-section.

The radiation beam PB is incident on the patterning device (e.g., maskMA), which is held on the support structure (e.g., mask table MT), andis patterned by the patterning device. Having traversed the mask MA, theradiation beam PB passes through the projection system PL, which focusesthe beam onto a target portion C of the substrate W. With the aid of thesecond positioner PW and position sensor IF (e.g. an interferometricdevice, linear encoder or capacitive sensor), the substrate table WT canbe moved accurately, e.g. so as to position different target portions Cin the path of the radiation beam PB. Similarly, the first positioner PMand another position sensor (which is not explicitly depicted in FIG. 1)can be used to accurately position the mask MA with respect to the pathof the radiation beam PB, e.g. after mechanical retrieval from a masklibrary, or during a scan. In general, movement of the mask table MT maybe realized with the aid of a long-stroke module (coarse positioning)and a short-stroke module (fine positioning), which form part of thefirst positioner PM. Similarly, movement of the substrate table WT maybe realized using a long-stroke module and a short-stroke module, whichform part of the second positioner PW. In the case of a stepper (asopposed to a scanner) the mask table MT may be connected to ashort-stroke actuator only, or may be fixed. Mask MA and substrate W maybe aligned using mask alignment marks M1, M2 and substrate alignmentmarks P1, P2. Although the substrate alignment marks as illustratedoccupy dedicated target portions, they may be located in spaces betweentarget portions (these are known as scribe-lane alignment marks).Similarly, in situations in which more than one die is provided on themask MA, the mask alignment marks may be located between the dies.

The depicted apparatus could be used in at least one of the followingmodes:

1. In step mode, the mask table MT and the substrate table WT are keptessentially stationary, while an entire pattern imparted to theradiation beam is projected onto a target portion C at one time (i.e. asingle static exposure). The substrate table WT is then shifted in the Xand/or Y direction so that a different target portion C can be exposed.In step mode, the maximum size of the exposure field limits the size ofthe target portion C imaged in a single static exposure.

2. In scan mode, the mask table MT and the substrate table WT arescanned synchronously while a pattern imparted to the radiation beam isprojected onto a target portion C (i.e. a single dynamic exposure). Thevelocity and direction of the substrate table WT relative to the masktable MT may be determined by the (de-)magnification and image reversalcharacteristics of the projection system PL. In scan mode, the maximumsize of the exposure field limits the width (in the non-scanningdirection) of the target portion in a single dynamic exposure, whereasthe length of the scanning motion determines the height (in the scanningdirection) of the target portion.

3. In another mode, the mask table MT is kept essentially stationaryholding a programmable patterning device, and the substrate table WT ismoved or scanned while a pattern imparted to the radiation beam isprojected onto a target portion C. In this mode, generally a pulsedradiation source is employed and the programmable patterning device isupdated as required after each movement of the substrate table WT or inbetween successive radiation pulses during a scan. This mode ofoperation can be readily applied to maskless lithography that utilizesprogrammable patterning device, such as a programmable mirror array of atype as referred to above.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

A further immersion lithography solution with a localized liquid supplysystem is shown in FIG. 4. Liquid is supplied by two groove inlets IN oneither side of the projection system PL and is removed by a plurality ofdiscrete outlets OUT arranged radially outwardly of the inlets IN. Theinlets IN and OUT can be arranged in a plate with a hole in its centerand through which the projection beam is projected. Liquid is suppliedby one groove inlet IN on one side of the projection system PL andremoved by a plurality of discrete outlets OUT on the other side of theprojection system PL, causing a flow of a thin film of liquid betweenthe projection system PL and the substrate W. The choice of whichcombination of inlet IN and outlets OUT to use can depend on thedirection of movement of the substrate W (the other combination of inletIN and outlets OUT being inactive).

Another immersion lithography solution with a localized liquid supplysystem solution which has been proposed is to provide the liquid supplysystem with a liquid confinement structure which extends along at leasta part of a boundary of the space between the final element of theprojection system and the substrate table. Such a system is shown inFIG. 5. The liquid confinement structure is substantially stationaryrelative to the projection system in the XY plane though there may besome relative movement in the Z direction (in the direction of theoptical axis). A seal is formed between the liquid confinement structureand the surface of the substrate. In an embodiment, the seal is acontactless seal such as a gas seal. Such a system with a gas seal isdisclosed in U.S. patent application Ser. No. 10/705,783, herebyincorporated in its entirety by reference.

FIG. 5 depicts an arrangement of a reservoir 10, which forms acontactless seal to the substrate around the image field of theprojection system so that liquid is confined to fill a space between thesubstrate surface and the final element of the projection system. Aliquid confinement structure 12 positioned below and surrounding thefinal element of the projection system PL forms the reservoir. Liquid isbrought into the space below the projection system and within the liquidconfinement structure 12. The liquid confinement structure 12 extends alittle above the final element of the projection system and the liquidlevel rises above the final element so that a buffer of liquid isprovided. The liquid confinement structure 12 has an inner peripherythat at the upper end preferably closely conforms to the shape of theprojection system or the final element thereof and may, e.g., be round.At the bottom, the inner periphery closely conforms to the shape of theimage field, e.g., rectangular though this need not be the case.

The liquid is confined in the reservoir by a gas seal 16 between thebottom of the liquid confinement structure 12 and the surface of thesubstrate W. The gas seal is formed by gas, e.g. air, synthetic air, N₂or an inert gas, provided under pressure via inlet 15 to the gap betweenliquid confinement structure 12 and substrate and extracted via firstoutlet 14. The overpressure on the gas inlet 15, vacuum level on thefirst outlet 14 and geometry of the gap are arranged so that there is ahigh-velocity gas flow inwards that confines the liquid. It will beunderstood by the person skilled in the art that other types of sealcould be used to contain the liquid.

Examination of test substrates exposed using an immersion lithographyapparatus with a liquid confinement structures having a circularcross-section has revealed that most of the drying stains and particlesleft on the substrate after exposures have been completed lie in thelocus of the side edges of the immersed region. In effect, theshowerhead leaves behind two tracks of drying stains and particles as itpasses across the substrate. See, e.g., the two tracks depicted in FIG.6.

The edges of the immersed space are typically not well defined and thereis a transition zone TZ, shown in FIG. 8, between areas that arecompletely dry and areas that are completely immersed (“wet”). The widthof the transition zone will depend on the exact dimensions and type ofthe liquid confinement system and may be present in all types of liquidsupply and/or confinement system, including those described herein. Thetransition zone may, at a minimum, be the width of the meniscus formedby the immersion liquid but may be wider than this due to turbulence,frothing, etc. in the immersion liquid because of gas flows used toconfine the liquid or used to sweep it away, for example.

In the transition zone, droplets of immersion liquid are continuallydeposited on the substrate. As shown in FIG. 6, the substrate is scannedrelative to the projection system PL and the liquid confinement systemin the direction of the arrow S. Droplets deposited on the substrate Win the leading edge of the transition zone will be swept up by the mainbody of liquid 11. Droplets deposited in the trailing edge of thetransition zone TZ will not be, but because the width of the transitionzone in this part is small, the time spent by a given point on thesubstrate in this zone is small and the probability of a droplet beingdeposited is low. On the other hand, a point on the substrate that ispassed over by the edge parts EZ of the transition zone will spend acomparatively long period in this zone and will not subsequently beswept over by the main body of the liquid. Thus, the probability of adroplet being deposited on the substrate and left behind after theliquid confinement system passes is high. Any particulates or dissolvedcontaminants in the liquid may then result in a drying stain or adeposited particulate when the immersion liquid evaporates.

According to an embodiment of the present invention, to reduce orminimize the occurrence of a drying stain and/or a deposited particulateon the substrate, the liquid confinement system is arranged to confinethe liquid to a space that is substantially polygonal in plan, ratherthan circular. This reduces or minimizes the time spent by a given pointin the transition zone. In a specific embodiment, a liquid confinementstructure 12 is used to confine the liquid 11 to the space and theliquid confinement structure has an inner periphery of the desiredpolygonal shape.

As shown in FIG. 7, in an embodiment of the invention, the immersionliquid is confined to a substantially square region 22 oriented with itsdiagonals substantially parallel to the principal axes X and Y of thesubstrate stage coordinate system. These principal axes are in effectdefined by the paths of measuring beams of the interferometricdisplacement measuring system IF, which measure displacements of thesubstrate table. It can be seen that if the substrate and liquidconfinement system are relatively moved (e.g., scanned) in directionsparallel to the X and/or Y axes, the length of the edge zone EZ′ in thedirection of motion is reduced/minimized and hence so is the probabilityof a particle being deposited or a drying stain forming.

It will be appreciated that the two or more corners of the polygon neednot be perfectly sharp. In an embodiment, two corners have a radius ofcurvature no greater than the width of the transition zone TZ, otherwisethe length of the edge zone EZ′ is increased. However, benefit may alsobe obtained with corners of larger radius, e.g. up to four or five timesthe width of the transition zone. If scanning movements of the substratewill be largely or exclusively in one direction, e.g. the Y direction,the shape of the space 22 need not be symmetrical as shown but could beshortened in the Y direction, so as to form a parallelogram or rhombus.The liquid confinement structure also need not be symmetrical about theX-axis so that a kite-shaped arrangement can be used. Curved, ratherthan straight edges may also be used. Some possible shapes are shown inFIG. 9. These shapes may further reduce the size of the edge zone EZ.The shape of the space to which the immersion liquid is confined is inprinciple only restricted by the need to ensure that the exposure fieldEF is completely covered by immersion liquid and to provide space toextract liquid as necessary.

In European Patent Application No. 03257072.3, the idea of a twin ordual stage immersion lithography apparatus is disclosed. Such anapparatus is provided with two tables for supporting a substrate.Leveling measurements are carried out with a table at a first position,without immersion liquid, and exposure is carried out with a table at asecond position, where immersion liquid is present. Alternatively, theapparatus has only one table

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,flat-panel displays, liquid-crystal displays (LCDs), thin-film magneticheads, etc. The skilled artisan will appreciate that, in the context ofsuch alternative applications, any use of the terms “wafer” or “die”herein may be considered as synonymous with the more general terms“substrate” or “target portion”, respectively. The substrate referred toherein may be processed, before or after exposure, in for example atrack (a tool that typically applies a layer of resist to a substrateand develops the exposed resist), a metrology tool and/or an inspectiontool. Where applicable, the disclosure herein may be applied to such andother substrate processing tools. Further, the substrate may beprocessed more than once, for example in order to create a multi-layerIC, so that the term substrate used herein may also refer to a substratethat already contains multiple processed layers.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.having a wavelength of or about 365, 248, 193, 157 or 126 nm).

The term “lens”, where the context allows, may refer to any one orcombination of various types of optical components, including refractiveand reflective optical components.

While specific embodiments of the invention have been described above,it will be appreciated that the invention may be practiced otherwisethan as described. For example, the invention may take the form of acomputer program containing one or more sequences of machine-readableinstructions describing a method as disclosed above, or a data storagemedium (e.g. semiconductor memory, magnetic or optical disk) having sucha computer program stored therein.

One or more embodiments of the present invention may be applied to anyimmersion lithography apparatus, in particular, but not exclusively, tothose types mentioned above. A liquid supply system is any mechanismthat provides a liquid to a space between the projection system and thesubstrate and/or substrate table. It may comprise any combination of oneor more structures, one or more liquid inlets, one or more gas inlets,one or more gas outlets, and/or one or more liquid outlets, thecombination providing and confining the liquid to the space. In anembodiment, a surface of the space may be limited to a portion of thesubstrate and/or substrate table, a surface of the space may completelycover a surface of the substrate and/or substrate table, or the spacemay envelop the substrate and/or substrate table.

The descriptions above are intended to be illustrative, not limiting.Thus, it will be apparent to one skilled in the art that modificationsmay be made to the invention as described without departing from thescope of the claims set out below.

1.-24. (canceled)
 25. A lithographic projection apparatus arranged toproject a pattern from a patterning device onto a substrate through aliquid, the apparatus comprising a liquid confinement structureconfigured to confine the liquid to a space adjacent the substrate,wherein the space is smaller in plan than the substrate, the space issubstantially polygonal in plan substantially parallel to the substrateand two corners of the space have a radius of curvature no greater thana width of a transition zone between the space configured to containliquid and a surrounding space configured not to have liquid.
 26. Theapparatus according to claim 25, wherein the space is a substantiallyregular polygon in plan.
 27. The apparatus according to claim 26,wherein the space is substantially square in plan.
 28. The apparatusaccording to claim 25, wherein diagonals of the space are respectivelysubstantially parallel to principal axes of a coordinate system of theapparatus.
 29. The apparatus according to claim 28, wherein theprincipal axes are substantially parallel or perpendicular to a beampath of a measuring system configured to measure displacement of thesubstrate table.
 30. A lithographic projection apparatus, comprising: anilluminator configured to condition a radiation beam; a supportconstructed to hold a patterning device, the patterning deviceconfigured to impart the radiation beam with a pattern in itscross-section to form a patterned radiation beam; a substrate tableconstructed to hold a substrate; a projection system configured toproject the patterned radiation beam onto a target portion of thesubstrate; and a liquid supply system configured to at least partly filla space between the projection system and the substrate with a liquid,the liquid supply system comprising a liquid confinement structureconfigured to at least partly confine the liquid within the space,wherein an inner periphery of the liquid confinement structure adjacentthe liquid substantially forms a polygon and two corners of the innerperiphery have a radius of curvature no greater than a width of atransition zone between the space configured to contain liquid and asurrounding space configured not to have liquid.
 31. The apparatusaccording to claim 30, wherein the inner periphery is substantially aregular polygon in plan.
 32. The apparatus according to claim 31,wherein the inner periphery is substantially square in plan.
 33. Theapparatus according to claim 30, wherein diagonals of the innerperiphery are respectively substantially parallel to principal axes of acoordinate system of the apparatus.
 34. The apparatus according to claim33, wherein the principal axes are substantially parallel orperpendicular to a beam path of a measuring system configured to measuredisplacement of the substrate table.
 35. A device manufacturing method,comprising: supplying liquid to a space adjacent a substrate, whereinthe space is smaller in plan than the substrate, the space issubstantially polygonal in plan substantially parallel to the substrateand two corners of the space have a radius of curvature no greater thana width of a transition zone between the space containing liquid and asurrounding space not containing liquid; and projecting a patterned beamof radiation through the liquid onto the substrate.
 36. The methodaccording to claim 35, wherein the space is a substantially regularpolygon in plan.
 37. The method according to claim 36, wherein the spaceis substantially square in plan.
 38. The method according to claim 35,wherein diagonals of the space are respectively substantially parallelto principal axes of a coordinate system of a lithographic apparatusused to project the patterned beam.
 39. The method according to claim38, wherein the principal axes are substantially parallel orperpendicular to a beam path measuring displacement of a substrate tableof the lithographic apparatus holding the substrate.
 40. A devicemanufacturing method, comprising: at least partly confining a liquid toa space between a projection system of a lithographic apparatus and asubstrate using a liquid confinement structure, an inner periphery ofthe liquid confinement structure substantially forming a polygon and twocorners of the inner periphery having a radius of curvature no greaterthan a width of a transition zone between the space containing liquidand a surrounding space not containing liquid; and projecting apatterned beam of radiation through the liquid onto the substrate. 41.The method according to claim 40, wherein the inner periphery issubstantially a regular polygon in plan.
 42. The method according toclaim 41, wherein the inner periphery is substantially square in plan.43. The method according to claim 40, wherein diagonals of the innerperiphery are respectively substantially parallel to principal axes of acoordinate system of the lithographic apparatus.
 44. The methodaccording to claim 43, wherein the principal axes are substantiallyparallel or perpendicular to a beam path measuring displacement of asubstrate table of the lithographic apparatus holding the substrate. 45.A liquid confinement structure for a lithographic projection apparatusarranged to project a pattern from a patterning device onto a substratethrough a liquid, the liquid confinement structure configured to confinethe liquid to a space adjacent the substrate, wherein the space issmaller in plan than the substrate, the space is substantially polygonalin plan substantially parallel to the substrate and two corners of thespace have a radius of curvature no greater than a width of a transitionzone between the space configured to contain liquid and a surroundingspace configured not to have liquid.